I'd back up Mark's post, worth checking the fabric coupling.
I had the same symptoms recently of knocking on over run, and with clutch dipped, road speed dependant, but mine went away on application of the handbrake. I found one of the nuts on the fabric coupling completely loose (Incorrect type). meaning the fabric coupling was flailing, and rubbing on the handbrake in its 'home' position. Nuts tightened and the noise went, but i'll be replacing the fabric coupling anyway, and replacing the incorrect fixings, which are causing the fabric to crush and push out, thus causing the loosening.
Hope it's nothing too serious for you.
I had the same symptoms recently of knocking on over run, and with clutch dipped, road speed dependant, but mine went away on application of the handbrake. I found one of the nuts on the fabric coupling completely loose (Incorrect type). meaning the fabric coupling was flailing, and rubbing on the handbrake in its 'home' position. Nuts tightened and the noise went, but i'll be replacing the fabric coupling anyway, and replacing the incorrect fixings, which are causing the fabric to crush and push out, thus causing the loosening.
Hope it's nothing too serious for you.